Front Tucking In - Why?

[drunkenmunkey]

Morning,

Can anyone offer advice as to why I'm having to apply pressure on the inside bar just to hold the bike up in the corner? It's falling in and not much fun even on hot tarmac.

It's a KTM Superduke R 990 and has a pretty short wheelbase, it's always been twitchy and had issues with the back lifting and starting to come around on braking. I made the mistake of fiddling and put everything back to standard and set the sag, she's now stable in a line but at anything other than flat out she's a bugger to get to track round a bend without input.

Maybe too much sag at the back? Too much front compression damping? (I'm guessing). Any suspension/tyre/ track gurus who could offer advice?

[308mate]

drunkenmunkey said:

Morning,

Can anyone offer advice as to why I'm having to apply pressure on the inside bar just to hold the bike up in the corner? It's falling in and not much fun even on hot tarmac.

It's a KTM Superduke R 990 and has a pretty short wheelbase, it's always been twitchy and had issues with the back lifting and starting to come around on braking. I made the mistake of fiddling and put everything back to standard and set the sag, she's now stable in a line but at anything other than flat out she's a bugger to get to track round a bend without input.

Maybe too much sag at the back? Too much front compression damping? (I'm guessing). Any suspension/tyre/ track gurus who could offer advice?

Its hard to understand what you're experiencing given your description, I assume you've checked tyre pressures?

[orangefzr]

At a quick guess, rear height too high or too much preload on the rear

[black-k1]

Worth checking, in this order:

Tyre pressures;
Wheel and steering bearings;
Are the yokes dropped on the front forks?
Rear pre-load/ride height;

[drunkenmunkey]

Thanks for the replies, I'm not being clear so thought about it and it's oversteering i.e. the front always trying to turn tighter...

Bearings are OK and forks are as far down the yolk as they can be, KTM didn't see fit to include rear ride height adjustment for reasons unknown...I'll check the pressures again and the rear preload, it's slightly softer than the front but would have thought that would cause understeer?...

Edited by drunkenmunkey on Friday 20th April 10:57

[Pravus1]

Sound to me like the rear is too high or front too low.

I also find if you have the front too soft it will feel like it's falling over. Add 3 or 4 clicks of front compression and see how it feels.

[moto_traxport]

orangefzr said:

At a quick guess, rear height too high or too much preload on the rear

I'm thinking exactly the opposite.

If you've ridden custom or chop with low back end and raked out front end they do exactly this. The front contact patch is too far back in relation to head / fork angle and requires pressure on the inside bar.

[orangefzr]

moto_traxport said:

I'm thinking exactly the opposite.

If you've ridden custom or chop with low back end and raked out front end they do exactly this. The front contact patch is too far back in relation to head / fork angle and requires pressure on the inside bar.

Ah you have the benefit of the second explanation though, I went on the initial question

Edited by orangefzr on Friday 20th April 14:13

[pozi]

Does the 990 have a slipper clutch only I am pretty sure the previous 950 didn't??

If not there is a lot of engine breaking from a V-Twin engine which can make the back feel nervous if you are off the throttle mid bend in a low gear, but you can ride around it by getting on a neutral throttle early.

Unless this has just started happening, in which case ignore all of the above and check your suspension

[curlie467]

orangefzr said:

moto_traxport said:

I'm thinking exactly the opposite.

If you've ridden custom or chop with low back end and raked out front end they do exactly this. The front contact patch is too far back in relation to head / fork angle and requires pressure on the inside bar.

Ah you have the benefit of the second explanation though, I went on the initial question

Edited by orangefzr on Friday 20th April 14:13

Yeah yeah, of course

[orangefzr]

curlie467 said:

Yeah yeah, of course

If you read the op's original post he says he has to keep pressure on the inside bar, which means he is having to force the front end to lean into the corner which is the opposite of what he describes is actually happening you would be pressing the outside bar to stop the bike 'dropping further in .....

My understanding of front end 'tucking' means that the front wheel is loaded with too much weight normally due to too much preload or rear ride height making the front wheel feel like it's going to lose all of it's grip and just wanting to go straight on requiring you to keep more weight on the inside bar just to make it go around the corner

Edited by orangefzr on Friday 20th April 17:38

Edited by orangefzr on Friday 20th April 18:01

[poo at Paul's]

drunkenmunkey said:

Thanks for the replies, I'm not being clear so thought about it and it's oversteering i.e. the front always trying to turn tighter...

Bearings are OK and forks are as far down the yolk as they can be, KTM didn't see fit to include rear ride height adjustment for reasons unknown...I'll check the pressures again and the rear preload, it's slightly softer than the front but would have thought that would cause understeer?...

Edited by drunkenmunkey on Friday 20th April 10:57

So this pressure on the inside bar, is that you pushing it........if so that is why it is turning.! To stand the bike up you would be pushing on the outside bar, if it is turning too tight.
Could this be self inflicted?
Assuming not, it may be rear ride height or it could even be a poorly worn front tyre, or even rear. Are there any steps in their profile?

[orangefzr]

I think I would be setting the bike up again with the aid of a helper so you can get your full weight on the suspension and get a helper to measure the sag again..... There are a multitude of videos on youtube and suspension websites... The trick is the actual amounts of sag front and rear you set it up to

[Gavia]

Is tucking in the opposite of swapping out?

[moto_traxport]

orangefzr said:

If you read the op's original post he says he has to keep pressure on the inside bar, which means he is having to force the front end to lean into the corner which is the opposite of what he describes is actually happening you would be pressing the outside bar to stop the bike 'dropping further in

Nope. It's too stable. It's hard to turn initially and mid corner you have to push on the inside bar otherwise the bike wants to turn more that you want. If he's messed with the back shock it's too low / too soft / too much rebound damping.

I've test ridden hundreds of bikes whilst managing a bike tuney place for nearly 10 years (Öhlins / Racetech / Extremetech / Matris importers & tech centres) and you get to know what messes what up (fork sag & position / yoke offset / shock length / wheel dia / tyre profile) and when to listen to customer. When you know what you're looking for you can often feel it before you've left the car park.

It helps to pump the tyres up to 36f / 42r to feel changes made to geometry etc but my initial thought on the original description was 'too low at the back'. A 40mph steady state corner such as large roundabout on that particular bike shouldn't require excessive pressure on the bars - i.e. once you've got it into the corner you should be able maintain that 'set' by holding the throttle steady with forefinger & thumb and no left hand. It is equally possible to mess up the balance of a bike by having too much ride height but from initial description I don't think that's the case here.

[CarsOrBikes]

that sounds like the op is pushing the bar to stop it turning even tighter, not to get it to turn,

op you sau you put it to standard then say the forks are as low as they can go, so as this shortens the rake, especially on a long fork leg, then is this not the issue, causing the front to pull round early?

[mckeann]

CarsOrBikes said:

that sounds like the op is pushing the bar to stop it turning even tighter, not to get it to turn,
?

Pushing which bar to stop it turning ??? He said pushing the inside bar, so that's making it keep turning.

[curlie467]

orangefzr said:

curlie467 said:

Yeah yeah, of course

If you read the op's original post he says he has to keep pressure on the inside bar, which means he is having to force the front end to lean into the corner which is the opposite of what he describes is actually happening you would be pressing the outside bar to stop the bike 'dropping further in .....

My understanding of front end 'tucking' means that the front wheel is loaded with too much weight normally due to too much preload or rear ride height making the front wheel feel like it's going to lose all of it's grip and just wanting to go straight on requiring you to keep more weight on the inside bar just to make it go around the corner

Edited by orangefzr on Friday 20th April 17:38

Edited by orangefzr on Friday 20th April 18:01

Whoosh parrot

[curlie467]

moto_traxport said:

Nope. It's too stable. It's hard to turn initially and mid corner you have to push on the inside bar otherwise the bike wants to turn more that you want. If he's messed with the back shock it's too low / too soft / too much rebound damping.

I've test ridden hundreds of bikes whilst managing a bike tuney place for nearly 10 years (Öhlins / Racetech / Extremetech / Matris importers & tech centres) and you get to know what messes what up (fork sag & position / yoke offset / shock length / wheel dia / tyre profile) and when to listen to customer. When you know what you're looking for you can often feel it before you've left the car park.

It helps to pump the tyres up to 36f / 42r to feel changes made to geometry etc but my initial thought on the original description was 'too low at the back'. A 40mph steady state corner such as large roundabout on that particular bike shouldn't require excessive pressure on the bars - i.e. once you've got it into the corner you should be able maintain that 'set' by holding the throttle steady with forefinger & thumb and no left hand. It is equally possible to mess up the balance of a bike by having too much ride height but from initial description I don't think that's the case here.

Away with your knowledge and experience, we'll have none of that here!

[drunkenmunkey]

Fixed!

Front pressure was too low, what a muppet, my tyre pressure guage was gubbed, tried another and oops 28psi.

She's still a flighty beast but that's the fun and tracks round a corner again.

Judging from the comments, I need to work on my writing. The front was oversteering and I had to apply pressure to the inside bar to stop it naturally wanting to tighten the arc if the corner.

Thanks for the replies!